리튬이차전지용 복합전극 미세구조 분석 및 최적 바인더 설계

복합 전극, Composite electrode, 고분자 바인더, Polymeric binder, 접착력, Adhesion, SAICASNⅠ. Introduction 1 1.1 Roadmap on EV mileage & cell design 1 1.2 The importance of binders from a microstructure point of view 2 1.3 In-depth analysis of binders in electrodes: limitations and improvements 4 1.4 Reference 6 Ⅱ. Effects of binder entanglement and crystallinity on the adhesion 7 2.1 Introduction 7 2.2 Experiment 8 2.2.1 Polymeric binder solution preparation 8 2.2.2 Polymer properties measurement 8 2.2.3 Electrode preparation 9 2.2.4 Electrical resistance measurement 9 2.2.5 Adhesion measurement 9 2.2.6 Cell assembly 10 2.2.7 Cycle test 10 2.2.8 Morphological and compositional analysis 10 2.3 Results and discussion 10 2.4 Conclusion 20 2.5 References 22 Ⅲ. Effects of binder swelling due to liquid electrolyte impregnation on the adhesion 25 3.1 Introduction 25 3.2 Experiment 26 3.2.1 Electrode preparation 26 3.2.2 Polymer film preparation 26 3.2.3 Annealing 27 3.2.4 Crystalline phase characterization 27 3.2.5 Adhesion measurement 27 3.2.6 Electrical resistance measurement 29 3.2.7 Electrochemical test 29 3.2.8 Morphological analysis 29 3.3 Results and discussion 30 3.4 Conclusion 51 3.5 References 52 Ⅳ. Binder for fast chargeable electrode for lithium-ion battery 56 4.1 Introduction 56 4.2 Experiment 57 4.2.1 Materials 57 4.2.2 Preparation of alkali metal ion substituted CMC binders 57 4.2.3 Material characterizations 58 4.2.4 Electrode preparation 58 4.2.5 Molecular dynamics simulation 59 4.2.6 Formation of 3D electrode structures 60 4.2.7 Electrochemical performance prediction 60 4.2.8 Electrochemical test 62 4.3 Results and discussion 63 4.4 Conclusion 75 4.5 References 77 Ⅴ. Application: cohesion and adhesion measurement of MEA for automotive fuel cell 80 5.1 Introduction 80 5.2 Experiment 84 5.2.1 MEA preparation 84 5.2.2 Cohesive/adhesive measurement using SAICAS 85 5.2.3 Morphological analysis 94 5.2.4 Compositional analysis 94 5.3 Results and discussion 94 5.4 Conclusion 102 5.5 References 104DoctordCollectio

Toward understanding the real mechanical robustness of composite electrode impregnated with a liquid electrolyte

The mechanical robustness of highly loaded composite electrodes is important for ensuring the long-term reliability of high-energy-density secondary batteries. Considering that in real state, the electrodes in batteries are completely impregnated with electrolyte, the swelling of the polymeric binder must be carefully observed and controlled to maintain the electric connectivity within the electrode. However, the decrease in the cohesion/adhesion of electrodes caused by electrolyte impregnation has not been directly measured due to the absence of appropriate tools. Here, the surface and interfacial cutting analysis system and a specifically designed sample holder are well combined to realize this breakthrough measurement. When electrode is impregnated with a liquid electrolyte, not only the 12% increase in electrode thickness but also the greater than 74% decrease in cohesion/adhesion, which is caused by the swelling of the amorphous phase of the polymeric binders, is clearly observed. The large decrease in cohesion/adhesion can be greatly ameliorated by controlling both the degree of crystallinity and crystallite size of the polymeric binder through a simple annealing process. Thus, it believes that the measurement of the real cohesion and adhesion of composite electrodes can provide an innovative and practical way to secure the reliability of high-energy-density batteries. © 2020 Elsevier Ltd1

Protective effects of Camellia japonica flower extract against urban air pollutants

Abstract Background Exposure of skin to urban air pollutants is closely related to skin aging and inflammatory responses such as wrinkles formation, pigmentation spot, atopic dermatitis, and acne. Thus, a great deal of interest has been focused on the development of natural resources that can provide a protective effect to skin from pollutants. Methods The antioxidative activity of Camellia japonica flower extract (CJFE) was evaluated by 1,2-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) assay, and the inhibitory effect of CJFE by urban air pollutants-induced reactive oxygen species (ROS) production was determined in cultured normal human dermal fibroblasts (NHDFs). We additionally investigated the protective effects of CJFE against urban air pollutant using in vitro and ex vivo model. Results CJFE with high phenolic concentration showed antioxidative activity on scavenging capacity of 1,2-diphenyl-2-picrylhydrazyl (DPPH) radicals and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical cation in a concentration dependent manner. CJFE inhibited urban air pollutants-induced ROS generation, matrixmetalloproteinase-1 (MMP-1) production and a xenobiotic response element (XRE)-luciferase activity indicating the aryl hydrocarbon receptor (AhR) transactivation. In addition, CJFE showed an excellent protective activity against pollutants-induced deteriorating effect in ex vivo model. CJFE reduced the level of pollutants-induced malondialdehyde (MDA), lipid peroxidation marker, inhibited MMP-1 expression and increased collagen synthesis. It also reduced the cell numbers with pyknotic nuclei (mainly occurring in apoptosis) and detachment of dermo-epidermal junction (DEJ) induced by pollutants. Conclusions Apparently, it is proposed that CJFE can be used as a protective material against pollutant-induced skin damages

The effects of humidity on the self-discharge properties of Li(Ni1/3Co1/3Mn1/3)O-2/graphite and LiCoO2/graphite lithium-ion batteries during storage

To investigate the effects of the exposure of battery tabs to humidity on the self-discharge properties of full-cell type lithium-ion batteries (LIBs), we assembled two different types of LIBs, composed of NCM/graphite or LCO/graphite, and compared their discharge retention abilities after storage in humid conditions (90% relative humidity (RH)) with and without battery tab protection. Regardless of the type of cathode active materials, tab protection improved the calendar lives of LIBs. For NCM/graphite, battery tab protection shows an approximate 50% improvement in the discharge capacity compared to the case without battery tab protection after storage in humid conditions (51.1% and 34.6% of the initial discharge capacity for tab-protected and non-protected LIBs, respectively). In contrast, LCO/graphite reveals a smaller change in the discharge capacity retention for the same experimental condition because they show superior capacity retention abilities regardless of battery tab protection (85.6% and 82.0% retention of the initial discharge capacity for tab-protected and non-protected LIBs, respectively). We suggested that these results come from the induction effect of polar water molecules, which pulls electrons to the battery tab side, resulting in lithium ion loss from the graphene layers to the liquid electrolyte. © The Royal Society of Chemistry.1

Mechanical robustness of composite electrode for lithium ion battery: Insight into entanglement & crystallinity of polymeric binder

To investigate the correlation between the molecular weight of the polymeric binder in Li-ion battery electrodes and their adhesion properties, polyvinylidene fluoride (PVdF) with three different molecular weights of 500,000, 630,000, and 1,000,000 are selected for LiCoO2 electrode fabrication. Using a surface and interfacial cutting analysis system, it is observed that, as the molecular weight of the PVdF increases, the adhesion strength not only in the electrode composite, but also at the electrode/current collector interface increases. This enhancement can be attributed to the increased polymeric chain entanglement and higher crystallinity of PVdF with higher molecular weight, which is confirmed using a microfluidic viscometer and differential scanning calorimeter, respectively. In summary, regardless of slightly higher electrode resistance, the LiCoO2 electrode with a PVdF binder of high molecular weight shows better electrochemical performance during cycling test even at 60 °C due to its stable mechanical integrity. © 2019 Elsevier Ltd1

Preplanting Nanosilica into Binderless Battery Electrodes for High-Performance Li-Ion Batteries

The energy density of Li-ion batteries (LIBs) can be effectively enhanced by increasing the thickness of a LiNixMnyCo1-x-yO2 (NMC) electrode and limiting the use of inactive components. However, the deficiency of a binder in thick NMC cathodes causes mechanical failure, such as crack formation and delamination, resulting in performance deterioration. To address the detrimental issues associated with thick electrodes, this study proposes the preplanting of nanosilica (SiO2) into a NMC composite electrode. SiO2 preplanted in the PVDF polymer solution can alter the viscoelastic properties of the NMC slurry and regulate the binder distribution within the NMC cathode. A lower binder concentration at the interface assisted by SiO2 preplanting enhances the charge transfer without compromising adhesion. The hydrophilic nature of fumed SiO2 can facilitate the penetration of the electrolyte through a thick NMC cathode, enhancing its high-power capability up to 4 C-rate. Owing to the HF scavenging role of fumed SiO2, the SiO2 preplanted cathode exhibited stable cycling at an elevated temperature (60 °C) by alleviating the side reactions triggered by salt decomposition. © 2023 American Chemical Society.FALS

Time‐Effective Accelerated Cyclic Aging Analysis of Lithium‐Ion Batteries

We propose a time-effective framework for accelerated cyclic aging analysis of lithium-ion batteries. The proposed framework involves the coupling of a physico-chemical capacity-fade model that considers the cyclic aging mechanisms of the LiMn2O4/graphite cell, with a physics-based porous-composite electrode model to predict cycling performance at different temperatures. A one-dimensional simple empirical life model is then developed from the coupled physico-chemical capacity-fade model and the physics-based porous-composite electrode model predictions. An accelerated cyclic aging analysis based on the principle of time-temperature superposition is performed using the developed one-dimensional simple life empirical model. The proposed framework is used to predict the maximum number of cycles and the highest temperature required for accelerated cyclic aging analysis of LiMn2O4/graphite cells. The efficacy of the proposed framework is validated with experimental cycle-performance data obtained from LiMn2O4/graphite coin cells at 25 and 60 °C. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim1

Semi-empirical long-term cycle life model coupled with an electrolyte depletion function for large-format graphite/LiFePO4 lithium-ion batteries

To overcome the limitation of simple empirical cycle life models based on only equivalent circuits, we attempt to couple a conventional empirical capacity loss model with Newman's porous composite electrode model, which contains both electrochemical reaction kinetics and material/charge balances. In addition, an electrolyte depletion function is newly introduced to simulate a sudden capacity drop at the end of cycling, which is frequently observed in real lithium-ion batteries (LIBs). When simulated electrochemical properties are compared with experimental data obtained with 20 Ah-level graphite/LiFePO4 LIB cells, our semi-empirical model is sufficiently accurate to predict a voltage profile having a low standard deviation of 0.0035 V, even at 5C. Additionally, our model can provide broad cycle life color maps under different c-rate and depth-of-discharge operating conditions. Thus, this semi-empirical model with an electrolyte depletion function will be a promising platform to predict long-term cycle lives of large-format LIB cells under various operating conditions. © 2017 Elsevier B.V.1

A coupled chemo-mechanical model to study the effects of adhesive strength on the electrochemical performance of silicon electrodes for advanced lithium ion batteries

A coupled chemo-mechanical model which considers the contact resistance as well as the influence of the attractive forces inside the contact area between the electrode and current collector was developed to evaluate the effects of the adhesive strength of a binding material on the electrochemical performance of silicon-based lithium-ion batteries. The increase in contact resistance between the electrode and current collector was introduced as a factor that reduces the electrochemical performance of the cell. The model predictions were validated with experimental data from coin-type half-cells composed of Li metal, Si electrodes, and Cu current collectors coated with binding materials with different adhesive strengths. The contact resistance increased with an increasing number of cyclic current rate. The adhesive strength decreased with cyclic current rate. The proposed model was used to investigate the effects of adhesive strength and various cell design parameters on the specific capacity of the Si-based Li-ion cells

Highly improved thermal stability of the ceramic coating layer on the polyethylene separator via chemical crosslinking between ceramic particles and polymeric binders

The ceramic coating layer (CCL) on a polyolefin separator plays a pivotal role in securing the safety of lithium-ion batteries (LIBs) by suppressing the thermal shrinkage of the separator even under abnormal circumstances. However, an additional CCL inevitably leads to energy density loss and electrochemical performance degradation. To mitigate these weaknesses, we designed a new chemical crosslinking between ceramic particles and polymeric binders to minimize the thickness of the CCL while maintaining its thermal stability. For this purpose, a polydopamine (PD) nanolayer is preliminarily introduced on the surface of ceramic particles using a simple solution polymerization method. Then, a poly(acrylic acid) binder, which can react with the amine groups in the PD, is chosen for the aqueous ceramic coating slurry. Thus, this combination can create a number of crosslinking points within the CCL, which leads to higher adhesion within the CCL after electrolyte impregnation. As a result, the crosslinked PD ceramic-coated separator (xPD-CCS) can maintain its original dimension even at 160 °C for 1 h with a 9-μm polyethylene base film. In addition, a full cell (LiNi0.8Co0.1Mn0.1O2/graphite) with the xPD-CCS can show a comparable cycle performance (capacity retention of 89.2% after 400 cycles) to those of bare polyethylene and non-crosslinked PD-CCS cases. © 2022 Elsevier B.V.1